Ubuntu Manpage: sg_verify - invoke SCSI VERIFY command(s) on a block device

Provided by: sg3-utils_1.46-3ubuntu4_amd64

NAME

       sg_verify - invoke SCSI VERIFY command(s) on a block device

SYNOPSIS

       sg_verify  [--0]  [--16] [--bpc=BPC] [--count=COUNT] [--dpo] [--ff] [--ebytchk=BCH] [--group=GN] [--help]
       [--in=IF] [--lba=LBA] [--ndo=NDO] [--quiet] [--readonly] [--verbose] [--version] [--vrprotect=VRP] DEVICE

DESCRIPTION

Sends one or more SCSI VERIFY (10 or 16) commands to DEVICE. These SCSI commands are defined in the SBC-2
and SBC-3 standards at http://www.t10.org and SBC-4 drafts.

When --ndo=NDO is not given then the verify starts at the logical block address given by the --lba=LBA
option and continues for --count=COUNT blocks. No more than --bpc=BPC blocks are verified by each VERIFY
command so if necessary multiple VERIFY commands are sent. Medium verification operations are performed
by the DEVICE (e.g. assuming each block has additional EEC data, check this against the logical block
contents). No news is good news (i.e. if there are no verify errors detected then no messages are sent to
stderr and the Unix exit status is 0).

When --ndo=NDO is given then the --bpc=BPC option is ignored. A single VERIFY command is issued and a
comparison starts at the logical block address given by the --lba=LBA option and continues for
--count=COUNT blocks. The VERIFY command has an associated data-out buffer that is NDO bytes long. The
contents of the data-out buffer are obtained from the FN file (if --in=FN is given) or from stdin. A
comparison takes place between data-out buffer and the logical blocks on the DEVICE. If the comparison is
good then no messages are sent to stderr and the Unix exit status is 0. If the comparison fails then a
sense buffer with a sense key of MISCOMPARE is returned; in this case the Unix exit status will be 14.
Messages will be sent to stderr associated with MISCOMPARE sense buffer unless the --quiet option is
given.

In SBC-3 revision 34 the BYTCHK field in all SCSI VERIFY commands was expanded from one to two bits. That
required some changes in the options of this utility, see the section below on OPTION CHANGES.

OPTIONS

Arguments to long options are mandatory for short options as well. The options are arranged in
alphabetical order based on the long option name.

-0, --0
a buffer NDO bytes long full of zeros is sent as the data-out part of a VERIFY command. So stdin
is not read and if --in=IF is given, an error is generated. Useful when BCH is 3 to check if some
or all of DEVICE (e.g. a disk) is zero filled blocks.

-S, --16
uses a VERIFY(16) command (default VERIFY(10)). Even without this option, using an --lba=LBA which
is too large, will cause the utility to issue a VERIFY(16) command.

-b, --bpc=BPC
this option is ignored if --ndo=NDO is given. Otherwise BPC specifies the maximum number of blocks
that will be verified by a single SCSI VERIFY command. The default value is 128 blocks which
equates to 64 KB for a disk with 512 byte blocks. If BPC is less than COUNT then multiple SCSI
VERIFY commands are sent to the DEVICE. For the default VERIFY(10) BPC cannot exceed 0xffff
(65,535) while for VERIFY(16) BPC cannot exceed 0x7fffffff (2,147,483,647). For recent block
devices (disks) this value may be constrained by the maximum transfer length field in the block
limits VPD page.

-c, --count=COUNT
where COUNT specifies the number of blocks to verify. The default value is 1 . If COUNT is greater
than BPC (or its default value of 128) and NDO is not given, 0 or less than multiple SCSI VERIFY
commands are sent to the device. Otherwise COUNT becomes the contents of the verification length
field of the SCSI VERIFY command issued. The sg_readcap utility can be used to find the maximum
number of blocks that a block device (e.g. a disk) has.

-d, --dpo
disable page out changes the cache retention priority of blocks read on the device's cache to the
lowest priority. This means that blocks read by other commands are more likely to remain in the
device's cache.

-E, --ebytchk=BCH
sets the BYTCHK field to BCH overriding the value (1) set by the --ndo=NDO option. Values of 1, 2
or 3 are accepted for BCH however sbc3r34 reserves the value 2. If this option is given then
--ndo=NDO must also be given. If BCH is 3 then NDO should be the size of one logical block (plus
the size of some or all of the protection information if VRP is greater than 0).

-f, --ff
a buffer NDO bytes long full of 0xff bytes is sent as the data-out part of a VERIFY command. So
stdin is not read and if --in=IF is given, an error is generated. Useful when BCH is 3 to check if
some or all of DEVICE (e.g. a disk) is 0xff byte filled blocks.

-g, --group=GN
where GN becomes the contents of the group number field in the SCSI VERIFY(16) command. It can be
from 0 to 63 inclusive. The default value for GN is 0. Note that this option is ignored for the
SCSI VERIFY(10) command.

-h, --help
output the usage message then exit.

-i, --in=IF
where IF is the name of a file from which NDO bytes will be read and placed in the data-out
buffer. This is only done when the --ndo=NDO option is given. If this option is not given then
stdin is read. If IF is "-" then stdin is also used.

-l, --lba=LBA
where LBA specifies the logical block address of the first block to start the verify operation.
LBA is assumed to be decimal unless prefixed by '0x' or a trailing 'h' (see below). The default
value is 0 (i.e. the start of the device).

-n, --ndo=NDO
NDO is the number of bytes to obtain from the FN file (if --in=FN is given) or from stdin. Those
bytes are placed in the data-out buffer associated with the SCSI VERIFY command and NDO is placed
in the verification length field in the cdb. The default value for NDO is 0 and the maximum value
is dependent on the OS. If the --ebytchk=BCH option is not given then the BYTCHK field in the cdb
is set to 1.

-q, --quiet
suppress the sense buffer messages associated with a MISCOMPARE sense key that would otherwise be
sent to stderr. Still set the exit status to 14 which is the sense key value indicating a
MISCOMPARE .

-r, --readonly
opens the DEVICE read-only rather than read-write which is the default. The Linux sg driver needs
read-write access for the SCSI VERIFY command but other access methods may require read-only
access.

-v, --verbose
increase the level of verbosity, (i.e. debug output).

-V, --version
print the version string and then exit.

-P, --vrprotect=VRP
where VRP is the value in the vrprotect field in the VERIFY command cdb. It must be a value
between 0 and 7 inclusive. The default value is zero.

BYTCHK

       BYTCHK is the name of a field (two bits wide) in the VERIFY(10) and VERIFY(16) commands. When set to 1 or
       3  (sbc3r34  reserves  the value 2) it indicates that associated with the SCSI VERIFY command, a data-out
       buffer will be sent for the device (disk) to check. Using the --ndo=NDO option sets the BYTCHK field to 1
       and NDO is the number of bytes placed in the data-out buffer. Those bytes are obtained from stdin  or  IF
       (from  the  --in=FN option). The --ebytchk=BCH option may be used to override the BYTCHK field value of 1
       with BCH.

       The calculation of NDO is left up to the user. Its value depends on the logical block size (which can  be
       found  with the sg_readcap utility), the COUNT and the VRP values. If the VRP is greater than 0 then each
       logical block will contain an extra 8 bytes (at least) of protection information.

       When the BYTCHK field is 0 then the verification process done by the device (disk) is vendor specific. It
       typically involves checking each block on the disk against its error  correction  codes  (ECC)  which  is
       additional data also held on the disk.

       Many  Operating Systems put limits on the maximum size of the data-out (and data-in) buffer. For Linux at
       one time the limit was less than 1 MB but has been increased somewhat.

OPTION CHANGES

       Earlier versions of this utility had a --bytchk=NDO option which set the  BYTCHK  bit  and  set  the  cdb
       verification length field to NDO.  The shorter form of that option was -B NDO. For backward compatibility
       that  option  is still present but not documented. In its place is the --ndo=NDO whose shorter form of -n
       NDO.  --ndo=NDO sets the BYTCHK field to 1 unless that is overridden by the --ebytchk=BCH.

NOTES

       Various numeric arguments (e.g. LBA) may include multiplicative suffixes or be given in hexadecimal.  See
       the "NUMERIC ARGUMENTS" section in the sg3_utils(8) man page.

       The amount of error correction and the number of retries attempted before a block is considered defective
       are  controlled in part by the Verify Error Recovery mode page. A note in the SBC-3 draft (rev 29 section
       6.4.9 on the Verify Error Recovery mode page) advises that to minimize the number of  checks  (and  hence
       have the most "sensitive" verify check) do the following in that mode page: set the EER bit to 0, the PER
       bit  to  1,  the DTE bit to 1, the DCR bit to 1, the verify retry count to 0 and the verify recovery time
       limit to 0. Mode pages can be modified with the sdparm utility.

       The SCSI VERIFY(6) command defined in the SSC-2 standard and later (i.e.  for tape drive systems) is  not
       supported by this utility.

EXIT STATUS

       The exit status of sg_verify is 0 when it is successful. When BCH is other than 0 then a comparison takes
       place  and  if it fails then the exit status is 14 which happens to be the sense key value of MISCOMPARE.
       Otherwise see the EXIT STATUS section in the sg3_utils(8) man page.

       Earlier versions of this utility set an exit status of 98 when there was a MISCOMPARE.

AUTHORS

       Written by Douglas Gilbert.

REPORTING BUGS

       Report bugs to <dgilbert at interlog dot com>.

COPYRIGHT

       Copyright © 2004-2019 Douglas Gilbert
       This software is distributed under a FreeBSD license. There is NO warranty; not even for  MERCHANTABILITY
       or FITNESS FOR A PARTICULAR PURPOSE.